Quantum-splitting oxide-based phosphors and method of producing the same

ABSTRACT

Strontium, calcium, strontium calcium, strontium calcium magnesium, calcium magnesium aluminates, and strontium borates activated with Pr 3+  exhibit characteristics of quantum-splitting phosphors under VUV excitation. A large emission peak at about 405 nm under VUV excitation is used conveniently to identify quantum-splitting phosphors. Improvements may be achieved with addition of fluorides or boric acid as a flux during the preparation of the phosphors. It is also possible to predict improvement in quantum efficiency by observing the ratio of emission intensities at about 480 nm and about 610 nm.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is related to patent applications Ser. No.09/681,666 (Attorney Docket No. RD-28342), titled “ImprovedQuantum-Splitting Oxide-Based Phosphors, Methods of Producing, and Rulesfor Designing the Same,” filed on May 18, 2001.

FEDERAL RESEARCH STATEMENT

This invention was first conceived or reduced to practice in theperformance of work under a contract with the United States Departmentof Energy, said contract having the contract number ofDE-FC26-99FT40632. The United States of America may have certain rightsto this invention.

BACKGROUND OF INVENTION Field of the Invention

This invention relates to oxide-based materials that have oneapplication as phosphors. More particularly, the phosphors arealuminates or borates doped with Pr³⁺ and exhibit quantum splitting whenirradiated with vacuum ultraviolet (“VUV”) radiation. This inventionalso relates to a method of making such quantum-splitting phosphors.

The conversion of a single ultraviolet (“UV”) photon into two visiblephotons with the result that the quantum efficiency of luminescenceexceeds unity is termed quantum splitting. Quantum splitting materialsare very desirable for use as phosphors for lighting applications, suchas fluorescent lamps. A suitable quantum splitting phosphor can, inprinciple, produce a significantly brighter fluorescent light source dueto higher overall luminous output because it can convert to visiblelight the part of UV radiation that is not absorbed efficiently bytraditional phosphors currently used in commercial fluorescent lamps.Quantum splitting has been demonstrated previously in fluoride- andoxide-based materials. A material comprising 0.1% Pr³⁺ in a matrix ofYF₃ has been shown to generate more than one visible photon for everyabsorbed UV photon when excited with radiation having a wavelength of185 nm. The measured quantum efficiency of this material was 140%, andthus greatly exceeded unity. However, fluoride-based compounds do nothave sufficient stability to permit their use as phosphors influorescent lamps because they are known to react with mercury vaporthat is used in such lamps to provide the UV radiation and formmaterials that do not exhibit quantum splitting. In addition, producingfluoride-based materials presents a great practical challenge because itinvolves the use of large quantities of highly reactive and toxicfluorine-based materials.

The applicants recently disclosed oxide-based quantum splittingmaterials. U.S. Pat. No. 5,552,082 discloses a lanthanum magnesiumborate activated with Pr³⁺ ion. U.S. Pat. No. 5,571,4151 discloses astrontium magnesium aluminate activated with Pr³⁺ ion and chargecompensated with Mg²⁺ ion. Emission spectra of these materials exhibit alarge peak at about 405 nm which is characteristic of quantum splitting.However, these materials still exhibit a considerable emission in the UVwavelength range of less than 350 nm. This part of the emission reducesthe overall visible light output that otherwise can be higher.Therefore, it is desirable to provide oxide-based quantum-splittingphosphors that have higher quantum efficiency in the visible range thanthe prior-art quantum splitting materials. It is also desirable toprovide more energy-efficient light sources using quantum-splittingphosphors having higher quantum efficiency. It is further desirable toprovide method for making materials having high quantum splittingcapability.

SUMMARY OF INVENTION

The present invention provides oxide-based phosphors doped with Pr³⁺ion, which phosphors exhibit quantum splitting when irradiated with VUVradiation. VUV radiation as used herein is radiation having wavelengthshorter than about 215 nm. The oxide phosphors of the present inventionare oxides of aluminum or boron having positive counterions selectedfrom Group IIA of the Periodic Table. The phosphors of the presentinvention may be used in mercury vapor discharge lamps to provideenergy-efficient light sources.

In one aspect of the present invention, the oxide-based phosphors arestrontium or strontium calcium aluminates having the magnetoplumbitecrystal structure. The aluminates are doped with Pr³⁺ ion. Furthermore,it is advantageous to substitute some of the aluminum ions withmagnesium ions for the purpose of charge compensation when Pr³⁺ issubstituted on the Sr²⁺ sites. Such oxide-based phosphors of the presentinvention have a composition represented by Sr_(1−1.5y)Pr_(y)Al₁₂O₁₉,Sr_(1−x−1.5y)Ca_(x)Pr_(y)Al₁₂O₁₉, orSr_(1−x−z)Ca_(x)Mg_(z)Al_(12−z)Pr_(z)O₁₉ where 0<x<1, y is in the rangefrom about 0.005 to about 0.5, z is in the range from about 0.005 toabout 0.5, x+1.5y≦1, and x+z<1.

In another aspect of the present invention, the oxide-based phosphorsare calcium or calcium magnesium aluminates activated with Pr³⁺ ionhaving a composition represented by Ca_(1−z)Pr_(z)Al₁₂O₁₉,Ca_(1−z)Pr_(z)MgAl_(11.33)O₁₉, or Ca_(1−z)Pr_(z)MgAl₁₄O₂₃ where z is inthe range from about 0.005 to about 0.5. In all of these host lattices,the Pr³⁺ ion can be charge compensated by the Mg⁺ ion or by latticevacancies.

In another aspect of the present invention, the oxide-based phosphorsare strontium borate activated with Pr³⁻ having a compositionrepresented by Sr_(1+z)Pr_(z)B₄O₇ where z is in the range from about0.005 to about 0.5.

The present invention also provides a method of making improvedquantum-splitting aluminate or borate phosphors. The method comprisesthe steps of selecting a desired final composition of the phosphor;mixing together materials from the following two groups: (1) at leastone oxygen-containing compound of praseodymium and (2) materialsselected from the group consisting of oxygen-containing compounds ofstrontium, calcium, magnesium, aluminum, and boron so to achieve thedesired final composition; forming a substantially homogeneous mixtureof the selected compounds; and firing the substantially homogeneousmixture in a non-oxidizing atmosphere at a temperature and for a timesufficient to result in the desired composition and to maintain thepraseodymium ion in the 3+ valence state.

In another aspect of the present invention, the method further comprisesadding at least one compound selected from the group consisting offluoride salts of aluminum, calcium, and strontium in a quantitysufficient to act as a flux prior to the step of forming thesubstantially homogeneous mixture. When the oxide-based phosphor is aborate, a quantity of boric acid may be advantageously used, either inplace of or in combination with the fluoride salts, as the flux.

Other benefits of this invention may become evident by a perusal of thedescription and appended claims together with the attached drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing energy levels of Pr³⁺ ion.

FIG. 2 is an emission spectrum of an aluminate quantum-splittingphosphor of the present invention having the nominal composition ofCaMgAl_(11.33)O₁₉:Pr³⁺ where the element following the colons representsthe activator doped in the host lattice at a low level.

FIG. 3 is an emission spectrum of an aluminate quantum-splittingphosphor of the present invention having the nominal composition ofCaAl₁₂O₁₉:Pr³⁺.

FIG. 4 is an emission spectrum of a borate quantum-splitting phosphor ofthe present invention having the nominal composition of SrB₄O₇:Pr³⁺.

FIG. 5 is a schematic illustration of a lamp incorporating a phosphor ofthe present invention.

DETAILED DESCRIPTION

In general, the present invention provides oxide-based phosphorsactivated with Pr³⁺. More particularly, the phosphors are strontium,strontium calcium, strontium calcium magnesium, calcium, calciummagnesium aluminates and strontium borates activated with Pr³⁺ ions. Thedoping level for Pr³⁺ is typically in the range from about 0.005 toabout 0.5.

In one preferred embodiment of the present invention, the aluminatephosphors have a formula of Sr_(1−1.5y)Pr_(y)Al₁₂O₁₉,Sr_(1−x−1.5y)Ca_(x)Pr_(y)Al₁₂O₁₉, orSr_(1−x−z)Ca_(x)Mg_(z)Al_(12−z)Pr_(z)O₁₉ where 0<x<1, y is in the rangefrom about 0.005 to about 0.5, z is in the range from about 0.005 toabout 0.5, x+1.5y≦1, and x+z<1. More particularly, phosphors having thequantum-splitting behavior have been made that have composition ofSr_(0.9)Pr_(0.1)Al₁₂O₁₉, Sr_(0.9)Pr_(0.1)Mg_(0.1)Al_(11.9)O₁₉, andSr_(0.725)Ca_(0.175)Pr_(0.1)Al_(11.9)Mg_(0.1)O₁₉.

In another preferred embodiment of the present invention, the aluminatephosphors have a formula of Ca_(1−z)Pr_(z)Al₁₂O₁₉,Ca_(1−z)Pr_(z)MgAl_(11.33)O₁₉, or Ca_(1−z)Pr_(z)MgAl₁₄O₂₃ where z is inthe range from about 0.005 to about 0.5, more preferably from about0.005 to about 0.2, and most preferably from about 0.005 to about 0.1.

In another preferred embodiment of the present invention, theoxide-based phosphors have a formula of Sr_(1−z)Pr_(z)B₄O₇ where z is inthe range from about 0.005 to about 0.5, more preferably from about0.005 to about 0.2, and most preferably from about 0.005 to about 0.1.

In general, emission spectra of materials exhibiting quantum-splittingcapability show a characteristic peak at about 405 nm, which peak is aresult of the first visible photon emitted as the excited Pr³⁺ ionradiatively decays from the ¹S₀ energy level to the ¹I₆ energy level.Thus, an examination of the intensity-versus-wavelength spectrumprovides a convenient way of determining whether a material would bequantum splitting, as opposed to using the more time-consumingmeasurement of quantum efficiency.

Without limitation, the quantum-splitting behavior of phosphors isattributed to the VUV excitation of the Pr³⁺ ion within the oxidelattice. Therefore, oxides of the present invention should be processedso as to maintain praseodymium as Pr³⁺ ion within the oxide lattice.

FIG. 1 shows the energy levels of Pr³⁺ ion. Although the applicants donot wish to be bound by any particular theory, it is believed that thequantum-splitting phosphors of the present invention offer quantumefficiency higher than unity because the Pr³⁺ ion excited by VUV emitstwo visible photons as it decays back to its ground state through thefollowing process. The excited Pr³⁺ ion in the 4f5d band decaysnon-radiatively to the ¹S₀ state from which it radiatively decays to the¹I₆ energy level and concurrently emits the first visible photon. ThePr³⁺ then non-radiatively decays from the ¹I₆ energy level to the ³P₀energy level from which it further radiatively decays to ³H₄, ³H₅, ³H₆,and ³F₂ levels and concurrently emits the second visible photon.

EXAMPLE

A calcium magnesium aluminate phosphor of the present invention havingthe nominal composition CaMgAl_(11.33)O₁₉:Pr³⁺ was produced and testedfor quantum-splitting characteristic:Re following amounts of compoundsof calcium, praseodymium, magnesium, and aluminum were mixed togetherthoroughly:

[t1]

1.35 g CaCO₃

0.26 g Pr₆O₁₁

0.60 g MgO

8.66 g Al₂O₃

The mixture was fired at 1400° C. for 6 hours in an atmosphere generatedby the reaction products of a coconut charcoal and volatized compoundsfrom the decomposition of the oxides and carbonates. The fired materialwas reblended and further heat-treated at 1100° C. for 6 hours in anatmosphere of 1% (by volume) hydrogen in nitrogen to produce thephosphor.

FIG. 2 shows the room-temperature emission spectrum of this phosphorunder a VUV excitation at 185 nm. The spectrum shows a largecharacteristic peak at about 405 nm of quantum-splitting materials dueto the ¹S₀→¹I₆ transition of excited Pr³⁺ ions. Other transitions fromthe ³P₀ and ³P₁ levels to the ³H₄, ³H₅, ³H₆, and ³F₂ levels with theemission of the second visible photon are also evident in the spectrum.

FIG. 3 shows the room-temperature emission spectrum of CaAl₁₂O₁₉:Pr³⁺,another exemplary quantum-splitting phosphor of the present invention,under a VUV excitation of 185 nm. The large peak at about 405 nm ischaracteristic of a quantum-splitting phosphor, exhibiting the the¹S₀→¹I₆ transition of excited Pr³⁺ ions.

FIG. 4 shows the room-temperature emission spectrum of a strontiumborate quantum-splitting phosphor of the present invention having thecomposition of Sr _(0.99)Pr_(0.01)B₄O₇ under a VUV excitation of 185 nm.The spectrum shows a large characteristic peak at about 405 nm ofquantum-splitting materials due to the ¹S₀→₁I₆ transition of excitedPr³⁺ ions. This phosphor shows an intense emission at about 252 nm dueto the ¹S₀→¹F₄transition. Thus, this or other similar phosphors may beused advantageously to produce more energy-efficient mercury dischargelamps. Specifically, this quantum-splitting phosphor absorbs energy ofthe 185-nm mercury emission and emits energy at about 252 nm, which inturn is absorbed efficiently by conventional phosphors to producevisible light. Thus, the heretofore-wasted energy of the 185-nm mercuryemission is converted usefully to visible light with the result ofhigher luminous output.

According theoretical considerations (R. Pappalardo, “Calculated QuantumYields for Photon-Cascade Emission (PCE) for Pr³⁺ and Tm³⁺ In FluorideHosts,” 14 J. Luminescence 159-193 (1976), incorporated herein asreference) the ratio Ω₄/Ω₆ of the Judd-Ofelt parameters should be assmall as possible in order to achieve a high quantum efficiency fromquantum-splitting materials. In the ideal case, this ratio should bezero. This ratio can be estimated by determining the ratio I(³P₀→³H₄)/I(³P₀→³H₆) where I(³P₀→³H₄) and I(³P₀→³H₆) are the intensities ofemission from the transitions ³P₀→³H₄ and ³P₀→³H₆, respectively. Theapplicants discovered that this ratio decreases when aluminum fluoridewas used as a flux during the preparation of the phosphor or when Mg²⁺or Ca²⁺ is incorporated in the host lattice. Mg²⁺ is preferablyincorporated at the aluminum site in the host lattice when Pr³⁺ issubstituted for Sr²⁺. Table 1 shows the effect of these modifications toan aluminate host lattice in which the emission is in response to anexcitation with radiation having a wavelength of 446 nm.

TABLE 1 Composition I(³P₀ → ³H₄)/I(³P₀ → ³H₆) Sr_(0.9)Pr_(0.1)Al₁₂O₁₉2.11 Sr_(0.9)Pr_(0.1)Al_(11.9)Mg_(0.1)O₁₉ 1.99Sr_(0.9)Pr_(0.1)Al_(11.9)Mg_(0.1)O₁₉ using a 2% AIF₃ 1.85 fluxSr_(0.725)Ca_(0.175)Pr_(0.1)Al_(11.9)Mg_(0.1)O₁₉ 1.82

Although the applicants do not wish to be bound by any particulartheory, it is believed that the fluoride ion in the flux substituted forsome of the oxygen ions. Therefore, it is expected that any fluoridesalt would offer the desired effect. For example, calcium, magnesium, orstrontium fluoride also would be effective. Furthermore, these fluorideshave the additional benefit of providing some of the desired cations forthe host lattice synthesis.

A quantum-splitting phosphor of the present invention is made in aprocess comprising the steps of; (1) selecting the desired finalcomposition of the phosphor such that the phosphor is activated bypraseodymium; (2) mixing together at least oxygen-containing compound ofpraseodymium and materials selected from the group consisting ofoxygen-containing compounds of strontium, calcium, aluminum, boron, andmagnesium in quantities so as to achieve the desired final compositionof the phosphor; (3) forming a homogeneous mixture of the selectedcompounds; and (4) firing the homogeneous mixture in a non-oxidizingatmosphere at a temperature and for a time sufficient to result in thedesired composition and to maintain the praseodymium ion in the 3+valence state. The oxygen-containing compounds used in the process maybe selected from the group consisting of oxides, carbonates, nitrates,sulfates, acetates, citrates, oxalates, and combinations thereof. Theoxygen-containing compounds may be in the hydrated or non-hydrated form.In a preferred embodiment, the process further comprises adding anamount of at least one material selected from the group consisting offluorides of aluminum, calcium, strontium, and magnesium before the stepof forming the substantially homogeneous mixture in a quantitysufficient to serve as a flux for the preparation of the oxide-basedphosphor. In another preferred embodiment, when the desired phosphor isa borate a quantity of boric acid is added into the mixture as a flux.The non-oxidizing atmosphere is generated from materials selected fromthe group consisting of carbon monoxide, carbon dioxide, hydrogen,nitrogen, ammonia, hydrazine, amines, and combinations thereof. Thefiring may be done in any suitable high-temperature equipment in eithera batch-wise or a continuous process. The firing may be doneisothermally. Alternatively, the process temperature may be ramped fromambient temperature to and then held at the firing temperature. Thefiring temperature is in the range from about 800° C. to about 2000° C.,preferably from about 850° C. to about 1700° C., and more preferablyfrom about 850° C. to about 1400° C. The firing time should besufficiently long to convert the mixture to the final desiredcomposition. This time also depends on the quantity of materials beingprocessed and the rate and quantity of non-oxidizing materials beingconducted through the firing equipment. A typical firing time is lessthan 10 hours.

A phosphor of the present invention characterized by quantum-splittingbehavior in VUV radiation and stability with regard to an environment ina mercury discharge device may be utilized as a phosphor in afluorescent lamp. FIG. 5 shows a lamp 50 comprising an evacuated housing60, a VUV radiation generating means 70 located within housing 60, and aphosphor 80 located within housing 60 and adapted to be excited by VUVradiation. In a preferred embodiment, lamp 50 is a fluorescent lamp andevacuated housing 60 comprises an evacuated glass tube and associatedend caps 62. VUV-generating means 70 is a combination of mercury vaporand means for generating high-energy electrons to create a mercury vapordischarge to excite the phosphor. The means for generating high-energyelectrons may be a filament of a metal having a low work function, suchas tungsten, or such a filament coated with alkali earth metal oxides asare known in the art. The filament is coupled to a high-voltage sourceto generate electrons from the surface thereof. A quantum-splittingphosphor of the present invention may be used in combination with otherconventional phosphors used in fluorescent lighting technology. Forexample, a quantum-splitting phosphor of the present invention may becombined with conventional red-, green-, and blue-phosphors to producewhite light from a mercury discharge lamp. Since the quantum-splittingphosphor of the present invention is transparent to the mercury 254-nmemission line, it may be coated on top of the conventional phosphorlayer in the lamp housing so to absorb substantially the mercury 185-nmemission line, thereby increasing the energy efficiency of the dischargelamp.

While specific preferred embodiments of the present invention have beendescribed in the foregoing, it will be appreciated by those skilled inthe art that many modifications, substitutions, or variations may bemade thereto without departing from the spirit and scope of theinvention as defined in the appended claims.

What is claimed is:
 1. An oxide-based quantum-splitting phosphorcomprising an oxide of aluminum and counterions of calcium andmagnesium; said oxide being doped with only Pr³⁺ ion; said Pr³⁺ ionacting as an activator in said phosphor; and said phosphor exhibiting aquantum-splitting behavior when irradiated by VUV radiation.
 2. Anoxide-based quantum-splitting phosphor having a formula selected fromthe group consisting of Sr_(1−1.5y)Pr_(y)Al₁₂O₁₉,Sr_(1−x−1.5y)Ca_(x)Pr_(y)Al₁₂O₁₉, andSr_(1−x−z)Ca_(x)Mg_(z)Al_(12−z)Pr_(z)O₁₉, wherein 0<x<1, y is in therange from about 0.005 to about 0.5, z is in the range from about 0.005to about 0.5, x+1.5y≦1, and x+z<1.
 3. An oxide-based quantum-splittingphosphor having a formula selected from the group consisting ofCa_(1−z)Pr_(z)Al₁₂O₁₉, Ca_(1−z)Pr_(z)MgAl_(11.33)O₁₉, andCa_(1−z)Pr_(z)Al₁₄O₂₃ where z is in the range from about 0.005 to about0.5.
 4. An oxide-based quantum-splitting phosphor having a formulaselected from the group consisting of Ca_(1−z)Pr_(z)Al₁₂O₁₉,Ca_(1−z)Pr_(z)MgAl_(11.33)O₁₉, and Ca_(1−z)Pr_(z)Al₁₄O₂₃ where z is inthe range from about 0.005 to about 0.5, wherein a charge of hostlattice upon incorporating Pr³⁺ ions in said host lattice is compensatedby further incorporating Mg²⁺ ions or lattice vacancies in said hostlattice.
 5. An oxide-based quantum-splitting phosphor having a formulaSr_(1−z)Pr_(z)B₄O₇, wherein z is in the range from about 0.005 to about0.5.
 6. An oxide-based quantum-splitting phosphor comprising an oxide ofan element selected from the group consisting of aluminum and boron, andat least one positive counterion selected from the group consisting ofstrontium, calcium, and magnesium; said oxide being doped with Pr³⁺ions; said phosphor exhibiting a quantum-splitting behavior whenirradiated by VUV radiation; and said phosphor being further doped withfluoride ions.
 7. A method of making a quantum-splitting phosphor, saidmethod comprising the steps of: (1) selecting a desired finalcomposition of said phosphor such that said phosphor is activated bypraseodymium ion; (2) mixing together: (a) at least oneoxygen-containing compound of praseodymium; (b) materials selected fromthe group consisting of oxygen-containing compounds of strontium,calcium, aluminum, boron, and magnesium; and (c) at least one fluorideselected from the group consisting of fluorides of aluminum, calcium,strontium, and magnesium; (3) forming a substantially homogeneousmixture of said oxygen-containing compounds and said fluoride; and (4)firing said substantially homogeneous mixture in a non-oxidizingatmosphere at a temperature and for a time sufficient to result in saiddesired final composition and to maintain substantially all of saidpraseodymium ions in a 3+ valence state.
 8. The method of claim 7wherein said non-oxidizing atmosphere is generated from materialsselected from the group consisting of carbon monoxide, carbon dioxide,hydrogen, nitrogen, ammonia, hydrazine, amines, and mixtures thereof. 9.The method of claim 7 wherein said firing is done isothermally at atemperature from about 800° C. to about 2000° C.
 10. The method of claim7 wherein said temperature is in a range from about 850° C. to about1700° C.
 11. The method of claim 10 wherein said firing continues for atime less than about 10 hours.
 12. The method of claim 7 wherein saidfiring is done while said temperature is ramped from ambient to an endtemperature in a range from about 850° C. to about 1400° C.
 13. Themethod of claim 12 wherein said firing continues for a time less thanabout 10 hours.
 14. The method of claim 7 wherein said oxygen-containingcompounds are selected from the group consisting of oxides, carbonates,nitrates, sulfates, acetates, citrates, oxalates, and combinationsthereof.
 15. The method of claim 14 wherein said oxygen-containingcompounds are selected from the group consisting of compounds in ahydrated form, a non-hydrated form, and combinations thereof.
 16. Alight source comprising an evacuated housing; a VUV radiation sourcelocated within said housing; and a phosphor located within said housingand adapted to be excited by said VUV radiation source; said phosphorcomprising an oxide-based quantum-splitting phosphor selected from thegroup consisting of: (1) a first material which comprises an oxide ofaluminum and calcium; said first material being doped with only Pr³⁺;and (2) a second material which comprises an oxide of boron andstrontium; said second material being doped with only Pr³⁺; saidphosphor exhibiting quantum-splitting behavior when irradiated by VUV.17. A light source comprising an evacuated housing; a VUV radiationsource located within said housing; and a phosphor located within saidhousing and adapted to be excited by said VUV radiation source; saidphosphor comprising an oxide-based quantum-splitting phosphor and havinga formula selected from the group consisting ofSr_(1−1.5y)Pr_(y)Al₁₂O₁₉, Sr_(1−x−1.15y)Ca_(x)Pr_(y)Al₁₂O₁₉, andSr_(1−x−z)Ca_(x)Mg_(z)Al_(12−z)Pr_(z)O₁₉, wherein 0<x<1, y is in therange from about 0.005 to about 0.5, z is in the range from about 0.005to about 0.5, x+1.5y≦1, and x+z<1.
 18. A light source comprising anevacuated housing; a VUV radiation source located within said housing;and a phosphor located within said housing and adapted to be excited bysaid VUV radiation source; said phosphor comprising an oxide-basedquantum-splitting phosphor and having a formula selected from the groupconsisting of Ca_(1−z)Pr_(z)Al₁₂O₁₉, Ca_(1−z)Pr_(z)MgAl_(11.33)O₁₉, andCa_(1−z)Pr_(z)MgAl₁₄Pr_(z)O₂₃ where z is in the range from about 0.005to about 0.5.
 19. A light source comprising an evacuated housing; a VUVradiation source located within said housing; and a phosphor locatedwithin said housing and adapted to be excited by said VUV radiationsource; said phosphor comprising an oxide-based quantum-splittingphosphor and having a formula of Sr_(1−z)Pr_(z)B₄O₇, wherein z is in arange from about 0.005 to about 0.5.
 20. The light source of claim 16further comprising phosphors that emit at least one radiation selectedfrom the group consisting of red, green, and blue visible radiation whenexcited by a UV radiation.
 21. A light source comprising an evacuatedhousing; a VUV radiation source located within said housing; and aphosphor located within said housing and adapted to be excited by saidVUV radiation source; said phosphor comprising an oxide-basedquantum-splitting phosphor selected from the group consisting of: (1) afirst material which comprises an oxide of aluminum and calcium; saidfirst material being doped with only Pr³⁺; and (2) a second materialwhich comprises an oxide of boron and strontium; said second materialbeing doped with only Pr³⁺; said phosphor exhibiting quantum-splittingbehavior when irradiated by VUV; said light source further comprisingphosphors that emit at least one radiation selected from the groupconsisting of red, green and blue visible light.
 22. An oxide-basedquantum-splitting phosphor having a formula of CaAl₁₂O₁₉:Pr³⁺.
 23. Anoxide-based quantum-splitting phosphor having a formula of SrB₄O₇:Pr³⁺.24. An oxide-based quantum-splitting phosphor consisting of an oxide ofboron and counterions of strontium; said oxide being doped with Pr³⁺ions, and said phosphor exhibiting a quantum splitting behavior whenirradiated by VUV radiation.
 25. An oxide-based quantum splittingphosphor consisting of an oxide of aluminum and counterions ofstrontium, calcium, and magnesium; said oxide being doped with Pr³⁺ions; and said phosphor exhibiting quantum splitting behavior whenirradiated by VUV radiation.